<span class="inventory-message"
  v-if="product.availableInventory - cartCount(product.id) === 0"> //#A
All Out!  
</span>
<span class="inventory-message"
  v-else-if="product.availableInventory - cartCount(product.id) < 5"> //#B
  Only {{product.availableInventory - cartCount(product.id)}} left!
</span>
<span class="inventory-message"
  v-else>Buy Now!
</span>
